In copending patent application Ser. No. 09/076,422, filed May 12, 1998, and entitled "WAVEGUIDE WITH EDGE GROUNDING," now U.S. Pat. No. 6,072,375, the disclosure which is hereby incorporated by reference in its entirety, a waveguide structure included at least two dielectric layers having opposing, substantially planar faces and one intermediate signal path layer positioned between the faces. A conductive layer was formed on each of the opposing, substantially planar faces to form outer ground planes. At least one controlled impedance signal track was formed within the waveguide structure at the intermediate signal path layer. A plurality of conductive vias interconnected the ground planes and in one embodiment, a plurality of grounding lines interconnected the vias at the intermediate signal path layer. A conductive via was connected to all adjacent conductive vias outside the controlled impedance signal track to form an inner grounding line grid that was coplanar with the controlled impedance signal track to work in conjunction with the plurality of conductive vias for waveguide mode rejection.
The grounding lines could be formed as etched connections. In another aspect of that invention, there could be no grounding lines and the plurality of conductive vias could form a "sea" of vias that extend through the dielectric layers and interconnect the ground planes. An inner grounding line grid that is coplanar with the controlled impedance signal track could work in conjunction with the plurality or "sea" of vias for waveguide mode rejection. The controlled impedance signal track could be formed as a split branch controlled impedance signal track or as a number of separate controlled impedance signal tracks. The grounding lines could be coplanar with the controlled impedance signal tracks such that the grounding lines and conductive vias establish the etched grounding that not only enhances waveguide mode rejection, but also enhances shielding between various controlled impedance signal tracks.
In another aspect of the copending application, the waveguide structure includes two intermediate signal path layers with a signal path formed to cross from one intermediate signal path layer to the other intermediate signal path layer. The grounding lines could interconnect the vias at each of the intermediate signal path layers to form a grid that is coplanar with each of the intermediate signal path layers and signal paths.
The invention as disclosed and claimed was advantageous because it provided a waveguide structure that was advantageous over previous "waffle-line" technology. The waveguide of the present invention provided for high performance radio frequency (e.g., microwave) interconnects that could be built in a batch process for production line quantities. By using multilayer dielectric technology, such as the use of non-conductive dielectric layers, printed dielectric and/or circuit layer technology and low cost graphic fabrication processes could be used.
However, it would be advantageous if other features could be provided in a waveguide structure, such as different controlled impedance signal tracks formed at different layers and not interconnected to each other, and embedded devices, such as buried resistors. Additionally, it may not be desirable to extend all conductive vias to all layers.